I’m gonna chime in and say “neither”.
The Paladin is intrinsically tied to the “knight in shining armor” archetype, being a holy warrior of the Light. As cool as Void stuff can look, it’s fundamentally and thematically incompatible with the Paladin class, meaning the only way you could make it work would be to completely ignore everything that a Paladin is.
I could see room to explore a completely Void-inspired class. Technically we have four Leather-users, so from that perspective I could see the logic in saying “let’s do four classes to each type”, which of course opens the possibility up for a Void-themed Plate user.
But even so, I don’t know that it really seems that terribly interesting. I think the Demon Hunter has already struggled with its flavor and identity not being far enough removed from Warlocks and Rogues. The Evoker was released later, and managed to get a third spec before DH did; I think that speaks to how narrow the focus of that class is, and how irrelevant it feels now that the Legion is (seemingly) gone.
There’s already a Void-inspired Priest, and with Warlocks having the Voidwalker minion, I could see room for exploring Warlocks having a connection to the Void. I suppose the same could hold true for Demon Hunters (which could help them feel more relevant post-Legion). Death Knights have never had a connection to the Void, but I suppose there’s nothing that precludes them from getting some Void flavoring, either, even if it’s not my particular cup of tea (Void and Undeath are depicted as antagonistic forces to one another, but I don’t believe they are fundamentally incompatible in the way Light and Void are).